“It’s the trains!” Ryan Hollister yelled at his wife Laura as he stormed into their home in Turlock, California. For two weeks in 2017, they looked at data from their newly installed Raspberry Shake, a Raspberry Pi-powered instrument that detects how the ground moves in a specific location. Expecting to see the telltale motions of distant earthquakes, they instead saw peculiar cigar-shaped waveforms at regular intervals. “The biggest challenge,” says Laura Hollister, “was the noise.”
“I thought it was the toilet flush or the washing machine,” says Ryan Hollister, but simple tests of going to the toilet or doing laundry showed him wrong. As he sat in his car watching a train rattle through Turlock, he realized that the three tracks traversing this small California town could be causing this mysterious seismic noise. As soon as he got home, he retrieved the data from the Raspberry Shake. Sure enough, every strangely intense bead of seismic waves matched a train, with the waves with the highest amplitude correlating to the closest track’s schedule, just half a mile from home.
It wasn’t the last time their seismic listening device picked up signs of human activity. As COVID-19 engulfed our world, the Hollisters, a husband-wife team of earth science educators, noted that their Raspberry Shake registered far less activity than usual. The decline came at times when their street, a main artery to the local high school, should be buzzing with teenagers.
That change was far from limited to Turlock. Thomas Lecocq, a seismologist paying particular attention to the ubiquitous vibrations of the Earth, found a marked decrease in high-frequency noise on a permanent seismic station under his jurisdiction at the Royal Observatory of Belgium. This curious silence was quieter and longer than he had seen during the subdued days between Christmas and New Year, and coincided with the imprisonment of his country.
In the following months, Lecocq and 76 co-authors from around the world combed through data from seismic stations in more than 70 countries using Python code that Lecocq wrote especially for this purpose. In total, 268 stations had usable data, and 185 of those saw high-frequency seismic noise in urban regions drop by up to 50 percent. The changes came in lockstep with the shutdown of every country in response to COVID-19. When the signals of driving, construction work and even walking disappeared, Ian Nesbitt, one of Lecocq’s co-authors: “Maybe we can investigate this [geologic] signals that we couldn’t see before because it was masked by that noise. “
Many of the stations were high-quality research tools installed by university or government scientists. But 65 were small Raspberry Shakes, sitting in the homes and offices of scientists and hobbyists alike. It turns out that when people make a lot of noise, seismically, anyone with a spare Raspberry Pi and a few hundred dollars for a Raspberry Shake board and some sensors can see it.
Build your own seismic station
The basic recipe for a seismic station requires four ingredients: sensors to measure the Earth’s motion, a means to record the measurements, a long-term storage solution (local or off-site) and a power source, says Emily Wolin, Seismic Network Manager. for the US Geological Survey (USGS) Albuquerque Seismological Laboratory.
State-of-the-art seismic stations have numerous sensors that detect an immense frequency range and record the Earth’s motion in three directions: up-down, east-west and north-south. Digitizers and data loggers record the data accurately and provide it with a time stamp. To power the equipment, the most remote stations can use solar panels, with power requirements varying dramatically based on communication needs, Wolin says.
To add a new seismic station to an earthquake monitoring network, Wolin says scientists need to explore locations that take regional geology and potential noise sources into account – such as railways (the Hollister’s home would never have made the cut). With a list of candidate sites, they then identify and contact land owners for approval and secure access for construction, installation and subsequent maintenance.
Wolin explains that preparation can sometimes involve ‘renting an oil rig to drill hundreds of meters into bedrock’. In some cases, thermally sealed and watertight seismic vaults must be carefully constructed to house equipment so sensitive that they would otherwise pick up tiny changes in pressure and temperature. Vaults also help minimize annoying anthropogenic noise. Installing the sensor and electronics “isn’t rocket science,” said Sue Hough, a USGS seismologist, but “it does require special training.”
Each layer of complexity adds a new line to the account. Top versions of a seismic station can cost more than $ 10,000, excluding installation costs, according to Hough. Branden Christensen, CEO of Raspberry Shake, says that if those costs are included, installing a single seismic station could cost more than $ 100,000. Those prices are exclusively affordable for government agencies, research institutions and industry.
Raspberry Shakes, on the other hand, have basic versions of the same components at a fraction of the price. A Raspberry Shake PCB is only $ 100 and can be connected to almost any ethernet or wireless Raspberry Pi. ‘We thought people would have [Raspberry Pis] ”says Christensen,“ and we [designed Raspberry Shakes to] support them all. “
A seismic sensor, such as a geophone, connects to the Raspberry Shake board, which serves as an amplifier and digitizer. The output from the sensor comes in the form of voltage differentials which must be amplified and converted into a known voltage per speed. This conversion, called a gain, leaves the output in units of voltage, according to Nesbitt, who is also Raspberry Shake’s former chief scientist.
The Raspberry Shake digitizes this information and sends it to the Raspberry Pi for further processing and archiving. An 8 gigabyte microSD card, which Nesbitt describes as the Raspberry Pi’s hard drive, is included with every Raspberry Shake and comes pre-loaded with all Shake software. The Raspberry Pi houses the SD card and provides power for the entire seismic station. “[The Raspberry Pi] is the computer that underpins everything, ”says Nesbitt.
With a Raspberry Shake board, building your own seismic station from scratch becomes as easy as adding a sensor and plugging the Raspberry Pi into your outlet, although Christensen recommends making an enclosure (you can using lego bricks!) to protect it from the bumps. of the residents of your household.
If you’d rather not assemble your own sensors, Raspberry Shake creates several out-of-the-box options based on the number and type of sensors you want. Ready-to-use options, Hough says, package all of these components in a compact plexiglass box.
The Hollisters chose the ready-to-use Raspberry Shake 4D, which is available for less than $ 400. To install, Ryan Hollister says all they had to do was “level and align the axles”. point direction so it is oriented correctly, and connect. ” Easy if, well… pi (e).